Buy ripe tomatoes, but not over-ripe. Wash them and scald with boiling water. The peelings should slip off after scalding with very little work. Cut the tomatoes into small pieces and simmer (do not boil) until they are soft. Put them through the food mill or a colander with small holes that will not permit the seeds to pass. Salt very slightly and cool. The juice can be used fresh or canned. Cannot be frozen as it curdles.
Blender Juice: Tomato juice can be made in the blender by blending the tomatoes after they are cooked; first put in some juice, then add part of the tomatoes. Keep blending until all is blended. Salt slightly. I think the juice made in the food mill might be a little better, but the blender is faster. The food mill strains out the seeds, the blender grinds them into the juice.
Juice made from Tomato Paste or Sauce: Dissolve the paste in one quart of water; season to taste and boil four minutes. Cool and serve. It could be made without boiling, but I think the cooking gives a better taste and makes it safe.